Tremor Reduction by Deep Brain Stimulation Is Associated With Gamma Power Suppression in Parkinson's Disease.

Martijn Beudel,Keyoumars Ashkan,Alexander L Green,Tipu Aziz,Marwan Hariz,Wesley Thevathasan,Patricia Limousin,Thomas Foltynie,Ludvic Zrinzo,Simon Little,Marko Bogdanovic,Binith Cheeran,Peter Brown,Alek Pogosyan

doi:10.1111/ner.12297

Abstract

ObjectivesRest tremor is a cardinal symptom of Parkinson's disease (PD), and is readily suppressed by deep brain stimulation (DBS) of the subthalamic nucleus (STN). The therapeutic effect of the latter on bradykinesia and rigidity has been associated with the suppression of exaggerated beta (13–30 Hz) band synchronization in the vicinity of the stimulating electrode, but there is no correlation between beta suppression and tremor amplitude. In the present study, we investigate whether tremor suppression is related to suppression of activities at other frequencies.Materials and MethodsWe recorded hand tremor and contralateral local field potential (LFP) activity from DBS electrodes during stimulation of the STN in 15 hemispheres in 11 patients with PD. DBS was applied with increasing voltages starting at 0.5 V until tremor suppression was achieved or until 4.5 V was reached.ResultsTremor was reduced to 48.9% ± 10.9% of that without DBS once stimulation reached 2.5–3 V (t14 = −4.667, p < 0.001). There was a parallel suppression of low gamma (31–45 Hz) power to 92.5% ± 3% (t14 = −2.348, p = 0.034). This was not seen over a band containing tremor frequencies and their harmonic (4–12 Hz), or over the beta band. Moreover, low gamma power correlated with tremor severity (mean r = 0.43 ± 0.14, p = 0.008) within subjects. This was not the case for LFP power in the other two bands.ConclusionsOur findings support a relationship between low gamma oscillations and PD tremor, and reinforce the principle that the subthalamic LFP is a rich signal that may contain information about the severity of multiple different Parkinsonian features.

Highlights

Resting tremor is, in conjunction with bradykinesia, rigidity, and postural instability, one of the four cardinal symptoms of Parkin-§ Unit of Functional Neurosurgery, Sobell Department of Motor Neuroscience & Movement Disorders, UCL Institute of Neurology, Queen Square, London, UK;¶ Melbourne Brain Centre, Department of Medicine, Royal Melbourne Hospital, University of Melbourne, Melbourne, Victoria, Australia; and** The Bionics Institute, Melbourne, Victoria, Australia son’s disease (PD) [1]
The question we address here is whether changes in low gamma activity correlate with tremor suppression during deep brain stimulation (DBS)
Note that both tremor amplitude and low gamma (31–45 Hz) local field potential (LFP) activity are suppressed at higher stimulation voltages, suppression of tremor seems to lag behind both the voltage and gamma changes by a few seconds and re-emerges later than gamma power after stimulation had stopped

Summary

Introduction

In conjunction with bradykinesia, rigidity, and postural instability, one of the four cardinal symptoms of Parkin-. § Unit of Functional Neurosurgery, Sobell Department of Motor Neuroscience & Movement Disorders, UCL Institute of Neurology, Queen Square, London, UK;. ¶ Melbourne Brain Centre, Department of Medicine, Royal Melbourne Hospital, University of Melbourne, Melbourne, Victoria, Australia; and. ** The Bionics Institute, Melbourne, Victoria, Australia son’s disease (PD) [1]. Rest tremor affects ∼70% of patients and occurs at 4 to 6 Hz [2]. The pathological hallmark of PD is well established, namely progressive degeneration of midbrain dopaminergic neurons and their projections to the basal ganglia, and the striatum in particular [3], it is not clear how this relates to.

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